Process for the stabilization of unsaturated hydrocarbons



compounds increasingly Patented Oct. 9,1945

UNITED STATES PATENT OFFICE rnoonss roa THE s'rasinza'rron or nrnnocmonsUNSATURAT Walter A. Schulze,

Bartlesville, kla., assignor to Phillips Petroleum Company, acorporation Delaware No Drawing.

Application February 10, 1942, Serial N0. 430,279

6 Claims. (01; zoo-666.5)-

This invention relates to the treatment of unsaturated hydrocarbonswhich are susceptible to the catalytic effects of. certain metals andmetal salts which greatly alter the spontaneous or induced reactions ofsaid hydrocarbons. More spe-' ciflcally this invention relates to amethod of treating dioleflns, vinyl compounds and the like, said methodfurther including means of controlling the concentration of certainmetals and/or metal compounds in said hydrocarbons to control thecatalytic effects thereof. Y

, Recently certain diolefins and vinylcompounds' such as butadiene,isoprene, piperylene, and the like have, by virtue of their reactivity,become extremely useful in concentrated form for controlled and/orcatalytically induced polymerization by various methods. Some of thepolymers produced by these methods possess properties lization.Preformed polymers and non-volatile residues present difllculties inprocessing and "represent a loss of valuable raw material, whilepolymerization inhibitors obviously interfere with the conversion of theraw material in the various manufacturing steps. Thus,'the chemicalcharacteristics of the dioleflns and vinyl compounds as well as thenature of the ultimate uses make it necessary to producesame in are of.

purity and uniform reactivity. Of particular importance is the controlpableof extensive catalytic effects.

The stabilization of aliphatic diolefln concen trates and the likeduring production, storage, and shipment against prematurepolymerization may comprise the use of various antioxidants or otherspecific additiyes'capable of suppr peroxide and/or polymer formation.However, in the presence of dissolved metal compounds, the eifect ofsuch additives may be overbalanced'and the additives themselvesdestroyed-by the catalytic effect of the metal compounds. In order toimpart adequate stability under these circumstanceagthe netal compoundsmust be removed means of the staor deactivatedprior to or by billzing orpurifying treatment.-

It is an object of this invention process for the substantially completeremoval of will be evident from the following metal compounds fromdiolefin concentrates.

It is a further object of this invention to provide a process for theregulation of the concentration of metal salts in diolefln concentratesat any stage in the production and processing of said concentrates.

It is a still further provide reagents for object of this invention'tothe purification of dioleiin concentrates containing traces of metalcom-' pounds by means of which metal compounds are removed or theconcentration thereof is reduced to desirable low values. Said reagentsmay or may not. have the properties of inhibitors in addition to theirspecific reaction with metal compounds.- These and other objects andadvantages disclosure.

The occurrence of metalconipounds in diolefln concentrates may be due toa number of factors among which may be the tendency of diolefins andunsaturated hydrocarbons to form metal salt complexes. Traces of metalsalts may thus be retained from contact with metals and metal alloys aswell as with treating solutions,

of the concentration of dissolved metals and metal salts which are'ca-Pmduce and reagents of various kinds. In particular, when segregated andpurified with cuprous or other metal salt reagents, the unsaturatedhydrocarbons may retain traces of dissolved metal salts. Copper saltsand others such as manganese, chromium, zinc, nickel, tin, cadmium, and

lead salts may profoundly affect the stability and processingcharacterictics of a diolefln concentrate'employed in emulsion and othertypes of polymerization, and may even be added to dioleflns, vinylcompounds, and the like to inhibit premature polymerization.

The methods employed are generally of such a nature that impurities suchas sulfur, oxygen and nitrogen compounds are substantiallycompletelyremoved. For example, the-high temperature thermal or"catalytic dehydrogenation processes employed to hydrocarbons effectivelydestroy and remove sulfur and other impurities.

Therefore although the exact nature of the metal .salts re ed bydioleflnic hydrocarbons is not always known, hydrocarbon complexformation is usually indicated because of complete absence of compoundssuch as mercaptans, naphthenic acids,'cresols and the like ordinarilyresponsible for metal salt formation in hydrocarbons such as gasolineand kerosene.

I have now discovered that greatly, improved results maybe obtained bythe purification of diolefin or other highly unsaturated hydrocarbonconcentrates prior to utilization when said concentrates contain metalcompounds. The purification procedure which is found particularlyeifective comprises the treatment of the byto provide to drocarbonliquids with certain reaaents which for producing diol'eiinsthesubstantially.

mercaptans.

convert the metal compounds therein to oil-insoluble form or tosubstantially deactivated form. Deactivation may in some instances beaccomplished by reduction of the metal ion concentration to extremelylow and non-harmful levels. The diolefinic hydrocarbons treated by theprocess may or mai not receive an after-treatment to remove any excessof said reagents, depending upon the chemical nature and anti-oxidantproperties of said reagents.

I have noted that the dissolved copp r salts present in a diolcfinichydrocarbon liquid for any reason may be removed or satisfactorilyreduced in concentration to levels of about one part per million or lessby the addition of certain alkyl These mercaptans of'gen'eral formulaR-SH, where R. represents an alkyl group may be considered organicderivatives of hydrogen sulfide and form copper saltsby reaction of themetal with the active sulfhydryl grouping. The oil-solubility of thecopper mercaptides varies with the length of the carbon chain of thealkyl group. Thus, as copper sulfide is the least soluble inorganiccopper salt, copper methyl mercaptide is the least soluble mercaptide.Copper ethyl mercaptide is appreciably more soluble, although its actualsolubility figure is extremely low. The propyl, butyl and amylmercaptides are much more soluble, ranging up to values of the order of0.1 to 1 per cent or more by weight of the light hydrocarbons.

When the copper content of a hydrocarbon liq-/ uid exceeds thesolubility of an alkyl copper mercaptide, the addition of thecorresponding mercaptan results ina reductionof the copper con- I tent,with the maximum reduction resulting from the addition of methylmercaptan. In treating diolefinic liquids to remove dissolved copper,ethyl mercaptan produces a reduction to a value of about 0.1 part permillion, while methyl mercaptan produces a still lower value notdetectable with extremely sensitive analytical methods. While lesscomplete removal results with ethyl mercaptan, any catalytic eflectattributable to the dissolved copper ethyl mercaptide is apparentlyoften beneficial. v

The methyl and ethyl mercaptans have the added advantage of beingrelatively strong antioxidants in addition to the copper removalfunction. Therefore, if an excess of reagent is used in adjusting thecopper concentration to nonharmful values, added protection againstoxidation is afi' orded. In processing steps such as certain forms ofemulsion polymerization, these mercaptans are not harmful and areordinarily converted to inactive salts. I

When hydrogen sulfide is employed instead of methyl or ethyl mercaptan,the removal of copper through formation of copper sulfide issubstantially complete. However; hydrogen sulfide is less convenient'touse in the process because of its toxicity and corrosive qualities. Alsohydrogen sulfide may be oxidized to form freesulfur which in some casesmay not be a desirable impurity in the hydrocarbon liquid. When anafter-treatment is used subsequent to the removal of copper, both of themercaptans and hydrogen of about one part per million or less. Thesereagents are characterized by sulfhydryl groupings in which the hydrogenmay be replaced by a metal, although the reactivity of the said hydrogenmay be influenced or even due to the presence of adjacent polyvalentgroupings. Thus,

in several cases the sulfhydryl group is dependent on a tautomericrearrangement or enolization.

The preferred reagents in this group are (1) diphenylthiocarbazone,commonly called dithizone, (2) diethyldithiocarbamic acid or an alkalimetal salt thereof, (3) thioglycollic acid -p-aminonaphthalide(thionalide) and (4) '2-mercapto so i sulfide may be substantiallycompletely removed by an alkaline wash. v

In addition to the above-named reagents with active sulfhydrylgroupings, certain other more complex organic compounds form coppersalts benzothiazole. The formulas of these reagents are as follows:

c.m-N=N c-sn CtHr-NH-N Since all reagents in this group react withcopper through the sulfhydryl group, the reagents may be used in aqueoussolutions, preferably on the alkaline side in which case the hydrogenmay be replaced by an alkali metal ion. The copper salt formed when thehydrocarbon liquid is contacted therewith may be retained by andwithdrawn in the aqueous phase. In some cases, the reagent may be addeddirectly to the hydrocarbon liquid when the solubility is favorable. Ifdesired any excess reagent may then be removed subsequently by means ofan alkaline wash. When direct addition of a reagent is desired, asolution in a miscible solvent such as benzene is often employed.

To illustrate the results obtained in the stabilization or purificationof diolefinic liquids, the

following exemplary applications are provided.

EXAMPLE I A butadiene concentrate which been treated over a cuprouschloride reagent retained traces of dissolved copper salts equivalent toabout 1 part per million of copper. Two portions Table I followingstorage in steel containers.

Table I N c golygimml umopper ion aracber mph content teristics (12weeks) P. P. M.

1 Untreated butadiene 1 Poor.

2 Butadiene+0.01%CH;SH. 0.l Good.

3 Butadiene-H). 01% C,H SH.. 0.1 Do.

At the end of the storage period, smallamounts of the excess mercaptanreagents remained in the hydrocarbon liquid, but did not adverselyafl'ect the processing of the material.

- parently through .for reaction with copper.

In order to demonstrate further the beneficial results obtained byadjustment of the concentration of copper compounds in aliphaticdiolefin concentrates, a portion of a completely unsatuassema vantage ofthe anti-oxidant function ,of these -materials.

While I have specifically disclosed my have tion with regard to itsapplication to bu ene While the process of the present invention may bedirected primarily to the reduction of the copper content of diolefinconcentrates, an added advantage is the capacity of the preferredreagents to form salts with other heavy metals apthe same mechanismproposed This factor enables the co-precipitation and removal in manyinstances of traces of other heavy metals present in said diolefinconcentrates. The following tabulation exemplifies a number of reactionspossible with the aforesaid reagents, and illustrates the multipleefiects resulting from the proper choiceoi reagents for stabilizingdioleflnic liq-v uids containing heavy metals.

Table III Reagents operative (listed in order of reduction of metalcontent)- Methyl mercsptan; dithizone; thionalide. Ditiigzone.

0. Methyl mercaptan; meroaptobenzothiazole. (ammo um saltThionslldadithisone. Dithlgzone. o.

drogen sulfide, methyl;

rated Cs hydrocarbon'liquid containing over 5 hydrocarbons, it will beobvious that the process per centof diolefins was treated withsufiicient disclosed is applicable to other unsaturated hycopper oleateto produce a copper content of drocarbons and related compounds in whoseproabout parts per million. This liquid then duction and processing theproblem of heavy showed an increased tendency toward oxygen abmetal saltcontamination or inhibition is encounsorption. and the polymerizationcharacteristics 10 tered. Also, while the reagents described herein wereimpaired. Treatment of this material achave been rather specificallyidentified, the methcording to the present invention produced the od ofselection and the requisite chemical and eff ts list in he f l w xamplphysical characteristics exemplified render this M n feature of theinvention subject to modification l5 and extension within the scope ofthe disclosure. The C5 diolefln liquid containing both isopreneTherefore, no limitations are to be inferred ex-, and piperylene andsmall amounts of C5 oleflns p as defined in the appended im after theaddition of 100 parts per million of cop- I claim: per was divided intoa number of sample portions. 1. The process of substantially completelyre- The portions we e then treated respectively with 20 moving dissolvedcopper compounds in the form methyl and ethyl mercaptan and withslightly of cuprous salt-unsaturated hydrocarbon comalkaline aqueoussolutions of the above-described plexes from substantially pure liquidbutadiene complex reagents exhibiting an active metal saltwhichcomprises contacting said butadiene in forming sulfhydryl group. Theresults are listed liquid form with methyl mercaptan and thereby inTable Ii, below. 2o precipitating substantially all of the copper con-Table I1 r 1 as Number Sample Reagent Egg; ti n c h racistics a P. .P.M. 1 Untreated Ca dioleiln N 0 Good.

Sample Ely-100 P. P. M. copper ..do 100 Very poor 3 Sample 2) Dithizone(0.1 cod.

n Sodium dlethyl-dithiocarbamate.... 0.1 Do. Thlonalide l 0.1 Do. Sodiummercspto-henzothiasole 0. 1 Do. 7. Methyl mercaptsn 0. 1 Do. 8. Ethylmercaptsn 0. 1 Do.

tained in said copper compounds as insoluble copper methyl mercaptide,and separating said copper methyl mercaptide from the resultingbutadiene.

2. The process of substantially completely removing dissolved coppercompounds in the form of cuprous salt-unsaturated hydrocarbon complexesfrom substantially pure liquid butadiene which comprisescontacting saidbutadiene in liquid form with. a reagent consisting of a materialselected from the group consisting of hymethyl mercaptan and ethyldrogen sulfide,

thereby precipitating substanmeroaptan and tially all of the coppercontained in said copper compounds as insoluble copper salts. andseparating said suiting butadiene.

" 3. The process of substantially completely removing dissolved coppercompounds in the form of cuprous salt-unsaturated hydrocarbon com-,

plex'es from liquid low-boiling aliphatic diolefin hydrocarbonconcentrates consisting essentially of low-boiling aliphaticdiolefln inga conjugated concentration of hydrocarbon havnot .over 0.1 part perliquid form. with a reagentconsisting'of a material selected from thegroup consisting of hymercaptan and tially all of the copper containedin said copper compounds as insoluble copper salts, and separating saidinsoluble copper salts from the resulting diolefln concentrate.

4. The process of substantially completely removing dissolved coppercompounds in the form 76 of cuprous salt-unsaturated hydrocarboncominsoluble copper salts from the resystem of double bonds to a million.mercaptan and ethyl thereby precipitating substanpounds contained insaid 7 tect said concentrate against oxidation, separating saidinsoluble copper salts from the resultingplexes from liquid low-boilingaliphatic diolefln hydrocarbon concentrates consisting essentiallycipitating substantially all of the copper con tained in said coppercompounds as insoluble copper salts, employing in said treatment suchan-excess of said reagent over the copper comconcentrate as toprodioletln concentrate containing said excess of said reagent, andreagent to'remain in said diolefin concentrate and function therein asan antioxidant.

, 5. The process of substantally completely removing dissolved coppercompounds in the form or cuprcus salt-unsaturated hydrocarbon complexesfrom liquid. low-boiling aliphatic diolefln hydrocarbon concentratesconsisting essentially of low-boiling aliphatic diolefln hydrocarbonallowing said excess of said.

having a coniugated'. system of double bonds which comprises contactingsaid concentrate in liquid form with hydrogen sulfide and therebyprecipitating substantially all of the copper contained in said coppercompounds as insoluble copper sulfide, and removing said copper sulfidefrom the resulting diolefin concentrate.

8. The process of substantially completely removing dissolved coppercompounds in the form of cuprous salt-unsaturated hydrocarbon complexesfrom substantially pure liquid butadiene to a concentration of not over0.1 part per million and simultaneously protecting said butadieneagainst oxidation which comprises conin liquid form with methyl'mercaptan and thereby precipitating substantacting said butadienetialiy all of the copper contained in said copper compounds as insolublecopper methyl mercaptide. employing in said treatment such as excess ofmethyl mercaptan over the copper contained in said butadiene as toprotect said concentrate against oxidation, separating said insolublecopper methyl mercaptide from the resulting butadiene containing saidexcess of said methyl mercaptan, and allowing said excess or said methylmercaptan butadiene and. function therein oxidant.

wsuraa aiscnonza.

as an antito remain in" said

